It is known to cover the grip zone of writing instruments in a sleeve, generally made of a flexible plastics material, in order to improve writing comfort for the user. Nevertheless, certain difficulties arise in fitting and securing such a sleeve on the body of the writing instrument, which is generally made of a material that is different from that of the grip sleeve, such as a hard plastics material or metal, for example.
By way of example, in order to prevent the grip sleeve from moving longitudinally on the body, an annular setback is formed in the grip zone of the body and the tubular sleeve is received therein at least in part. However, it is generally necessary to provide a sleeve of elastic material of diameter that is slightly smaller than that of the annular setback so that the sleeve clamps onto the setback with a certain amount of force and so that the grip sleeve does not become removed in normal use.
This makes it more difficult to put the sleeve into place, in particular when assembly is performed automatically and the sleeve needs to be slid along the body over portions that present an outside diameter that is significantly greater than the diameter of the annular setback.
Furthermore, it is often preferable to prevent the sleeve from turning relative to the body, in particular in order to make the writing instrument feel more comfortable in the hand. For this purpose, provision is generally made to form projecting or indented portions in relief extending longitudinally along the annular setback of the body, with complementary portions in relief on the inside wall of the grip sleeve, so that cooperation between these portions in relief prevents the sleeve from turning. Nevertheless, the presence of such portions in relief complicates fabrication of the body and of the sleeve, and in general it is necessary to make provision for the sleeve to clamp onto the body quite firmly in order to ensure the portions in relief cooperate well. Document U.S. Pat. No. 5,971,644 describes means of that type for holding a grip sleeve stationary.
Certain grip sleeves are secured to the body during molding of those two parts in a mold using a dual-injection technique. Nevertheless, that molding technique is not easy to implement and generally significantly increases the cost of manufacture.